(1) Field of the Invention
This invention relates to a flat plate having excellent light transmittance, reduced moisture absorption and enhanced mechanical strength, and which is thin and becomes colored only to a negligible extent.
This flat plate is useful as a light guide plate and a light diffusion panel.
(2) Description of the Related Art
Characteristics such as a high light transmittance, a reduced thickness and a reduced distortion due to moisture absorption are required for light guide plates used as a liquid crystal base plate and a light diffuser panel. To provide a light guide plate having the required characteristics, for example, an injection-molded plate has been proposed in Japanese Unexamined Patent Publication No. H7-118344, which is made of a cycloolefin polymer having a norbornane ring structure, made by metathesis-catalyzed polymerization of 8-methyl-8-methoxycarbonyltetracyclododeca-3-ene, and having an intrinsic viscosity of 0.2 to 1.5 dl/g imparted thereto for enhancing the fluidity upon molding. However, this proposal has problems such that, (1) for enhancing the fluidity to provide a thin plate, when the molecular weight of the cycloolefin polymer is reduced, the mechanical strength of the plate is reduced, or the plate is cracked upon molding or becomes brittle, and, when the molding temperature is elevated, the molded plate becomes colored, and further that, in contrast, (2) when the molecular weight of the cycloolefin polymer is increased enough for improving the mechanical strength, the melt fluidity is decreased and a thin plate is difficult to obtain.